Effect of Ultrasonic Impact on Microstructure and Corrosion Resistance of CrCoFeNi High Entropy Alloy by Laser Melting Deposition

With gas atomized CrCoFeNi pre-alloyed powder with equal atomic ratio as raw materials, CrCoFeNi high entropy alloy was prepared by laser melting deposition, and was treated by ultrasonic impact technique. The effect of ultrasonic impact on the phase composition, microstructure, microhardness, residual stress and corrosion resistance of the high entropy alloy was investigated. The results show that after ultrasonic impact treatment, the high entropy alloy still had a single face centered cubic structure. After ultrasonic impact treatment, a plastic deformation layer formed on the surface, the orientation of dendrites changed from vertical to the alloy surface to approximately parallel to the surface, and the ultrafine grains, high-density dislocations and the twins formed on the surface. After ultrasonic impact treatment, the microhardness of the surface layer of alloy was improved the surface residual stress in the range of 0–500 µm from the alloy surface underwent a tensile-compression transition, and the surface residual compressive stress was the largest, reaching 230.8 MPa. After ultrasonic impact treatment, the self-corrosion potential of high entropy alloy increased, the self-corrosion current density decreased, the size and number of pitting corrosion pits decreased, and there was no stress corrosion characteristic; the corrosion resistance was improved.